I want to skip payment step in checkout. Later ask for payment and set payment status.
Maybe this example helps you? https://magento.stackexchange.com/questions/174023/how-to-disable-previous-checkout-step-when-goes-t...
This is the opposite but you'll find examples about how to extend the checkout steps (maybe this examples helps you to understand a little bit more the checkout steps structure): http://devdocs.magento.com/guides/v2.2/howdoi/checkout/checkout_new_step.html